"Four years ago, I was fab, fit and in my 40s with a dynamic marketing and media business, exciting social life and active sporting schedule. My lifestyle was exciting and affluent."

But devastating symptoms forced Sarah Dacre, now 50, to transform her life. She rarely leaves her house in north London, which she has screened from electromagnetic radiation with foil-lined wallpaper and Nasa-designed silvered cloth over the windows. She limits her computer use and makes telephone calls only on a landline. "If we go out for a quick meal we have to be out at seven and leave by eight because that's when everyone arrives with all their phones and their BlackBerrys," she adds.

Why? Because she is convinced that the cause of her symptoms is the electromagnetic fields (EMFs) emitted by computers, mobile phone handsets, cordless telephones, phone masts and the rest.

Bewildering symptoms

Faced with a bewildering array of symptoms - including hair loss, severe headaches, memory loss, insomnia, dizziness, heart palpitations, tinnitus and digestive problems - three doctors failed to diagnose and treat her illness. After 18 months of debilitating illness she made her own diagnosis, with the help of the internet. She believes she has developed electrosensitivity (ES).

Estimates of how many people suffer from it are scarce, but they range from 3.2% in California to 8% in Germany. In the UK around 4% of people claim to experience symptoms. "There's a lot of [ES sufferers] around," said Denis Henshaw, a physics professor who is head of the human radiation effects group at Bristol University. "They are otherwise sane and sensible people. They are not all nutcases."

Yet the scientific case for ES is almost non-existent. "I think the picture is getting more conclusive that it is not EMFs that are causing symptoms," says Dr James Rubin, a researcher at the Institute of Psychiatry in London. He has reviewed 31 studies into ES; none showed ES as a statistically significant cause of symptoms. "That still leaves open questions about what is the problem in that case. These people are certainly ill, and experience real symptoms."

The World Health Organisation backs up his view. A position statement drafted in December 2005 says: "There is no scientific basis to link ES symptoms to EMF exposure. Further, ES is not a medical diagnosis, nor is it clear that it represents a single medical problem."

The clearest data come from provocation studies, in which people who claim that, say, mobile phones make them ill are placed in a room with a mobile phone that is either on or off, and report to an researcher how they feel. Neither the patient nor the researcher knows when the phone is on. This double-blind condition eliminates the possibility that a sufferer might feel ill because of a psychological association between their symptoms and the phone's status.

The researchers later compare the timings of the worst headaches, for example, for any correspondence with the times when the patient was bathed in radiation from the mobile phone. The message from dozens of provocation studies is clear: EMFs, or "electrosmog" to the campaigners, do not cause the symptoms.

Dr Rubin's group published one such study in the prestigious British Medical Journal (tinyurl.com/yekoxp with criticism, and responses, at tinyurl.com/ydun89). It found no difference in reported effects, phone off or on. Dr Rubin suggests patients are experiencing an extreme "nocebo" effect: expecting something to make you unwell prompts real symptoms. This diagnosis is not very satisfying for sufferers. Rod Read, who runs a campaign group called electrosensitivity.org, says: "I find it really obnoxious to suggest that all of my 300 people are deluded. We reassure them that what they are experiencing is real."

He initially encouraged sufferers to help the scientists by participating in research, but now advises them not to. He said that several sufferers have dropped out of studies because they have been made worse. Rubin responds: "When [participants] do drop out, they are just as likely to drop out after a placebo [exposure] as after a genuine [exposure]. So even here there is no evidence for genuine sensitivity.

"Also, even without the most sensitive of the sensitive, the people who do take part in these studies still report severe symptoms, even though they are subsequently shown to be not due to the EMFs. There is no real reason to think that the mechanism for the symptoms is psychological in these people, but biological in the ones who don't take part."

Martin Röösli at the University of Berne in Switzerland said although drop-outs might affect the results, after more than 30 studies there should have been more positive data if something really is going on. "You always have these drop-outs. If these people dropped out only in the exposure condition and not in the sham condition this would be reported in the study," he said. In his own study, the drop-outs were evenly distributed between the real and false exposure conditions.

But Magda Havas, of Trent Unviersity in Ontario, Canada, says that scientists are demanding impossibly high standards of studies. "The medical community and the scientific establishment is very conservative," she says. "People doing novel research that begins to question the status quo have a very difficult time getting it published. Initially when you are working in a totally novel field you can't get money for that sort of research."

Others maintain that research on the chronic effects of EMFs - for example, research suggesting that living under power lines might double the risk of leukaemia in children (tinyurl.com/y9unnu) - means scientists should keep an open mind. "There's an enormous number of studies showing various forms of effects," says Olle Johansson at the Karolinska Institute in Stockholm. "It is of course of paramount importance to know exactly what is causing these problems."

Whatever the cause, some scientists believe that some organisations set up to help sufferers may actually be making things worse by encouraging them to take elaborate measures to avoid EMF exposure. These include moving beds to line up with magnetic north or changing from a metal-sprung mattress to a foam one. Some groups sell or advocate expensive devices for detecting or shielding from EMFs. Rubin and his colleagues noted: "A danger exists that [these adjustments] will reinforce a patient's view of himself or herself as being sensitive to electromagnetic fields and put him or her at risk of developing symptoms association with other electrical stimuli."

Benefit for patients

Stacey Eltiti, who is part of a team doing a provocation study at Essex University, says: "I think in some ways [self-help groups] can be helpful and in some ways be harmful ... If all the time sufferers are being perhaps told false information or information that has been spun to make them more fearful and perhaps not showing them all the facts, that can put them into a worse state."

One thing that everyone can agree on is that there needs to be more research into how to relieve the symptoms. Dr Rubin has reviewed nine studies into how to treat the condition. Four used cognitive behavioural therapy, two used computer screen filters, one looked at a shielding device and one studied acupuncture.

He and his colleagues concluded that although the quality of all the studies was limited, only cognitive behavioural therapy showed a benefit for patients. They are cautious, though, because in none of the four studies did the researchers have a true control treatment. The apparent beneficial effects on patients may simply have been due to spending extended periods with a sympathetic therapist.

For their part, the ES sufferers just want answers. "We are not unscientific or anti-scientific. We fully agree that there is not a scientific consensus," says Read. "We think the important question is how and why these people are suffering."

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